This invention relates to polishing curved surfaces. More particularly, it relates to the provision of a method and apparatus for polishing aspherical surfaces on optic lenses and the like.
Conventional methods of manufacturing progressive lenses requires the lens finisher to carry an inventory of semi-finished lens blanks consisting of a range of up to ten different front curves. Each curve group is divided into add powers ranging from +1 to +3 diopters in 0.25 diopter increments. The add power of each lens is positioned off center and so there must be semi-finished lens blanks for each eye. The cost of obtaining and maintaining the necessary inventory is substantial.
The finishing operation commences with the finisher selecting a pair of lens blanks with an appropriate base curve. Then, a spherical or toric surface is formed on the back surfaces of the lens blanks. These surfaces are then polished by use of equipment that requires a substantial inventory of laps including a spherical or toric polishing lap for each back surface curve. Alternatively, a polishing lap must be cut for each lens.
In order to lessen the inventory of polishing tools, several compromises are made in the manufacture of lenses in the manner described. Firstly, the lens finisher maintains an inventory of tools for only some of the lens shapes. The prescription for a particular lens is used to match the lens base curve with the closest available tool in inventory. The finisher tries to produce a lens that is as close as possible to the prescribed lens. The exact curve necessary to produce the prescribed power is seldom cut due to this compromise.
Compromises are also made in the production of toric lenses. Typically, back surface generation of a toric surface will produce an elliptical error of one meridian. A progressive, semi-finished lens, which has two different power curves, will have a toric surface including a single cylinder amount cut on the back rather than an appropriate cylinder amount for the distance and add portions.
Aspheric back surfaces on lenses can reduce spherical aberration errors on higher power lenses. They can also reduce edge thickness on high minus lenses and reduce center thickness on high plus lenses. Most of the common current methods of lens manufacture cannot economically produce a controlled aspheric back surface.
There is a need for a method and apparatus for economically polishing a large number of different curvature lens surfaces, particularly aspheric surfaces, by use of a small inventory of tools. There is also a need for a polishing method and apparatus that will permit the lens finisher to accurately mill a semi-finished lens blank, in order to provide a lens surface that closely conforms to the prescription, followed by accurate polishing of the milled surface.
The polishing methods in use today employ abrasive slurries. A first slurry contains coarse particles. A second slurry includes fine particles. This method is messy. Also, the coarse particles, used first, contaminate the equipment making it necessary to use two polishing machines, one with the more coarse particle slurry and the other with the finer particle slurry. There is a need for a polishing system which eliminates the mess and contamination of the slurry system and allows the use of a single machine for both coarse and fine polishing. There is also a need for such a system that will provide for a quick and automatic change between different grades of abrasive material.
There is also a need for a holder for a lens or other objects with a surface to be polished, that will permit an easy and firm connection of the object to the support prior to use, and a quick and easy removal of the object from the support after polishing. There is also a need for a lap having a lap wall that is adjustable in shape and curvature and will then hold the shape and curvature.
A principal object of the present invention is to provide a method and apparatus that fills all of the needs discussed above.
Prior art methods and apparatuses for polishing lens surfaces, including aspheric surfaces, existing in the patent literature, are disclosed by the following United States patents: U.S. Pat. No. 3,050,909, granted Aug. 28, 1962 to George O. Rawstron; U.S. Pat. No. 4,606,151, granted Aug. 19, 1986, to Erich Heynacher; U.S. Pat. No. 4,850,152, granted Jul. 25, 1989, to Erich Heynacher, Klaus Beckstette and Michael Schmidt; U.S. Pat. No. 4,979,337, granted Dec. 25, 1990, to Arthur G. Duppstabt; U.S. Pat. No. 4,980,993, granted Jan. 1, 1991, to Hideaki Umezaki; U.S. Pat. No. 5,095,660, granted Mar. 17, 1992, to Lawrence A. Dillon; U.S. Pat. No. 5,255,474, granted Oct. 26, 1993, to Tomohiro Gawa, Katsuyoshi Shingu and Kiyoshi Mayahara; U.S. Pat. No. 5,577,950, granted Nov. 25, 1996, to Kenneth L. Smith and Stephen Kulan; U.S. Pat. No. 5,593,340, granted Jan. 14, 1997, to Thomas E. Nelson and Erik A. Larsen; U.S. Pat. No. 5,632,668, granted May 27, 1997, to Gene O. Lindholm and Robert A. Follensbee; U.S. Pat. No. 5,762,546, granted Jun. 9, 1998, to Michael D. James and Fritz R. Kruis and U.S. Pat. No. 6,123,610, granted Sep. 26, 2000, to Erik A. Larsen. These patents should be carefully considered for the purpose of putting the present invention into proper prospective with the prior art.
The present invention includes the provision of a lens polishing system in which a polishing fabric is positioned between a surface to be polished and a lap wall having a shape complementary to the shape of the surface to be polished. The surface to be polished and the lap are held in fixed rotation position relative to each other. The polishing fabric is slide back and forth between them, across the surface to be polished, and the surface to be polished and the lap are rotating together relative to the polishing fabric. The present invention also relates to the components of the system, and to assemblies of the components.
The present invention includes providing a lap that includes a lap wall that is constructed from a material having a plastic first state and a substantially solid second state. When it is in its first state, the lap wall is formable to the curvature of the surface to be polished. It is moved relatively against the surface to be polished, causing it to assume a shape that is complementary in form and matching in shape to the shape of the surface to be polished. Once reshaped, the lap wall material is caused to assume its substantially solid second state in which it will retain the shape placed on it by the surface to be polished.
In one embodiment of the invention, the surface to be polished is a surface on a lens. A lens holder is provided and the lens is secured to the holder with the surface to be polished directed away from the holder. The present invention includes providing a vacuum lens holder adapted to hold the lens or other member in place on the holder.
The present invention includes providing a lap that comprises a rigid mounting ring and a lap wall within the confines of the mounting ring. The lap wall material is initially plastic and is moldable. While in a plastic state, the wall is pressed against a surface that is to be polished causing it to conform in shape to the surface to be polished. The lap wall is then caused to become substantially solid.
In a system of the invention, the surface to be polished is on a member that is secured to a support that is in turn secured to a frame. The lap wall is secured to a support that in turn is also secured to the frame. The frame is used to hold the surface to be polished and the lap wall in fixed positions, each to the other. A polishing fabric is positioned between the surface to be polished and the lap wall. The lap wall is positioned to hold the polishing fabric into contact with the surface to be polished. Then the polishing fabric is moved relatively across the surface to be polished and/or the surface to be polished is moved relatively across the polishing fabric. The polishing fabric acts to polish the surface to be polished while the lap guides movement of the polishing fabric across the surface to be polished.
The present invention also includes providing a support and guide frame for the polishing fabric that is positioned axially between the support for the member having a surface to be polished and the support for the lap. This frame has a peripheral portion that surrounds an open center. The polishing fabric sits on the peripheral portion and slides relative to the peripheral portion while staying in contact with it.
The present invention includes an embodiment in which the polishing fabric is in the form of a flexible and preferably elastic belt that rests on the support and guide frame and is connected to the drum. The drum is rocked about an axis, causing the polishing fabric to move sideways across the support and guide frame, first in one direction and then in the opposite direction. The drum is suitably rotated in one direction about its axis. It is then stopped and then rotated back in the opposite direction, so as to cause a back and forth movement of the polishing fabric over the support and guide frame and across the surface to be polished.
The present invention also includes providing a system in which the holder for the member having a surface to be polished. The lap, and the support and guide frame for the polishing fabric, are all mounted on a turntable so as to be movable back and forth about an axis in a way that causes the surface to be polished and the lap wall to rotate together around a common axis. The surface to be polished is in contact with the polishing fabric and the lap maintains the polishing fabric pressed substantially against the surface to be polished.
The present invention includes providing a polishing fabric composed of a flexible and preferably elastic fabric base and particles of an abrasive material that are bonded to a fabric base. In preferred form, the fabric base regions for particles that differ in coarseness, from coarse to fine. The polishing fabric lacks the messiness of a slurry. Also, the use of a fabric with plural regions of abrasive material makes it possible to perform the entire polishing operation by use of a single machine.
The present invention includes providing a vacuum holder for a lens or other member having a surface to be polished in which a backing is cast in situ behind a member having the desired rear surface shape of a member that is to be held by the holder and which becomes firm so that it possesses a front surface that conforms to such shape and curvature. The invention further includes providing a method of making the vacuum holder.
The present invention further includes providing a lap comprising a frame member that includes a socket, a support ring for a lap wall that is removably securable to the frame member, about the socket, and a lap wall that spans across the support ring and has a periphery that is connected to the support ring. The lap wall is constructed from a material that has a plastic state and a solid state. Fluid pressure is introduced into the socket, behind the lap wall, when the lap wall material in is its plastic state. The fluid pressure is used to force the plastic material outwardly against a surface on a member that has been provided outwardly of the lap wall, so that the lap wall will take on the shape and curvature of such surface. Then the lap wall material is caused to change from its plastic state to its solid state so that it will retain its form and surface shape and curvature.
These and other advantages, objects and features will become apparent from the following best mode description, the accompanying drawings, and the claims, all of which are incorporated herein as a part of the disclosure of the invention.